1. Field of the Invention
The present invention relates to a wafer transport module and, more specifically, to a door latch transmission mechanism for a module cover for wafer transport module, which can smoothly accurately be moved between the locking position and the unlocking position with less effort.
2. Brief Description of the Prior Art
Before becoming an IC chip, a wafer must be processed through a series of processing procedures including diffusion, printing, etching, masking, reading, and etc. Transport means are used in factory to deliver wafers from one working area to another. These transport means (cassette, boat, POD, or FOUP) are mainly to protect wafers against contamination of dust and external objects. FIG. 1 illustrates a transport means for this purpose. This transport means is constructed according to U.S. Pat. No. 5,915,562, issued to Nyseth et al., entitled xe2x80x9cTransport Module With Latching Doorxe2x80x9d. The wafer transport module 1 comprises a module body 10 and a module cover 20. The module body 10 is adapted to carry wafers W, having an opening 11 at one side thereof and a plurality of latch holes 13 disposed around the opening 11. The module cover 20 comprises an outer cover panel 21, and at least one door latch 27 respectively slidably disposed on the inside. The outer cover panel 21 of the module cover 20 comprises at least one lock cylinder hole 25 or rotary handle 253. An implement can be inserted to rotate each lock cylinder hole 25 and rotated to move the respective door latch 27 in and out of a corresponding peripheral through hole 23 of the module cover 20. Alternatively, the user can directly rotate the rotary handle 253 to move the respective door latch 27 in and out of the corresponding peripheral through hole 23 of the module cover 20. In order to let the module cover 20 close the opening 11 of the module body 10 tightly to protect storage wafers W against outside dust, the door latch 27 will be moved forwards (toward the corresponding latch hole 13) and then outwards (toward the outer cover panel 21) when extending out of the respective peripheral through hole 23, to engage the corresponding latch hole 13. To achieve this function, the door latch transmission mechanism of the aforesaid design comprises a rotary wheel 29. The rotary wheel 29 comprises a protruded center mount 293 aimed at one lock cylinder hole 25 on the outer cover panel 21 for receiving an implement being inserted into the lock cylinder hole 25 for enabling the rotary wheel 29 to be rotated by the implement, at least one first eccentric guide slot 295 and at least one second eccentric guide slot 296. The door latch 27 comprises a first latch 271 and a second latch 272. The first latch 271 has a front coupling rod 275 coupled to one first eccentric guide slot 296 of the rotary wheel 29. The second latch 272 has a front coupling rod 276 coupled to one second eccentric guide slot 296. When rotating the rotary wheel 29, the first latch 271 and the second latch 272 are respectively moved. The first latch 271 and the second latch 272 are arranged in a stack. After extended out of the respective peripheral through hole 23 (the X-axis direction), the first latch 271 is forced by the second latch 272 to move in Y-axis direction and to engage the corresponding latch hole 13. This design of door latch transmission mechanism has numerous drawbacks as outlined hereinafter.
1. Because the second latch forces the first latch into engagement with the corresponding latch hole, dust tends to be produced to contaminate storage wafers during friction between the first latch and the second latch.
2. Because the second latch rubs against the inner surface of the outer cover panel of the module cover during its movement, dust may be produced to contaminate storage wafers due to friction between the second latch and the inner surface of the outer cover panel.
3. During sliding movement of the door latch, much resistance is produced against the movement of the first latch and the second latch, and therefore much effort must be employed to rotate the rotary wheel.
4. Because the second latch is adapted to force the first latch into engagement with the corresponding latch hole, the first latch and the second latch must be will matched. Therefore, the fabrication of the component parts of the door latch transmission mechanism is complicated.
The invention has been accomplished under the circumstances in view. It is therefore the main object of the present invention to provide a module cover for a wafer transport module, which eliminates the aforesaid drawbacks. It is another object of the present invention to provide a module cover, which greatly reduces the production of dust when operated to close/open the wafer transport module. It is still another object of the present invention to provide a module cover for a wafer transport module, which can easily be opened and closed with less effort. It is still another object of the present invention to provide a module cover for a wafer transport module, which has a simple structure and, is inexpensive to manufacture. To achieve these and other objects of the present invention and according to one aspect of the present invention, the module cover assembly comprises a module cover and at least one door latch transmission mechanism adapted to lock/unlock the module cover. The at least one door latch transmission mechanism each comprises a door latch supported on a roller at the module cover, a latch bolt pivotally coupled between one end of the door latch and a part of the module cover, and a driving wheel coupled to the module cover and rotated to move the door latch forwards and backwards and to further turn the latch bolt in and out of a through hole on the module cover and a respective latch hole on the wafer transport module to lock/unlock the module cover. According to another aspect of the present invention, the driving wheel of each door latch transmission mechanism comprises a center mount coupled to a handle means that is disposed outside the module cover for operation by hand to rotate the driving wheel, and a smoothly arched eccentric guide slot; the door latch of each door latch transmission mechanism comprises an upright coupling rod disposed at one end and coupled to the smoothly arched eccentric guide slot of the respective driving wheel for enabling the door latch to be moved forwards and backwards by the respective driving wheel.